U.S. patent application number 10/536463 was filed with the patent office on 2006-10-12 for trans-thermoelectric device.
Invention is credited to Pratima Addepalli, RandallG Alley, Thomas Colpitts, KipD Coonley, Mary Napier, BrooksC O'Quinn, Michael Puchan, EdwardP Siivola, Rama Venkatasubramanian.
Application Number | 20060225773 10/536463 |
Document ID | / |
Family ID | 32393453 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060225773 |
Kind Code |
A1 |
Venkatasubramanian; Rama ;
et al. |
October 12, 2006 |
Trans-thermoelectric device
Abstract
A thermoelectric device having at least one unipolar couple
element (22) including two legs (22a) of a same electrical
conductivity type. A first-temperature stage (24) is connected to
one of the two legs. A second-temperature stage (28) is connected
across the legs of the at least one unipolar couple element. A
third-temperature stage (30) is connected to the other of the two
legs. Methods for cooling an object and for thermoelectric power
conversion utilize the at least one unipolar couple element to
respectively cool an object and produce electrical power.
Inventors: |
Venkatasubramanian; Rama;
(Cary, NC) ; Coonley; KipD; (Durham, NC) ;
Siivola; EdwardP; (Raleigh, NC) ; Puchan;
Michael; (Clayton, NC) ; Alley; RandallG;
(Raleigh, NC) ; Addepalli; Pratima; (Cary, NC)
; O'Quinn; BrooksC; (Lillington, NC) ; Colpitts;
Thomas; (Durham, NC) ; Napier; Mary;
(Carroboro, NC) |
Correspondence
Address: |
MYERS BIGEL SIBLEY & SAJOVEC
PO BOX 37428
RALEIGH
NC
27627
US
|
Family ID: |
32393453 |
Appl. No.: |
10/536463 |
Filed: |
November 25, 2003 |
PCT Filed: |
November 25, 2003 |
PCT NO: |
PCT/US03/37633 |
371 Date: |
March 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60428753 |
Nov 25, 2002 |
|
|
|
Current U.S.
Class: |
136/205 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01L 35/30 20130101; H01L 2924/0002 20130101; H01L 2924/0002
20130101; H01L 35/16 20130101; H01L 35/32 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
136/205 |
International
Class: |
H01L 35/30 20060101
H01L035/30 |
Claims
1. A thermoelectric device comprising: at least one unipolar couple
element having two legs of a same electrical conductivity type; a
first-temperature stage connected to one of said two legs; a
second-temperature stage connected across said legs of the at least
one unipolar couple element; and a third-temperature stage
connected to the other of said two legs.
2. The device of claim 1, wherein said at least one unipolar couple
element is configured such that currents flow in opposite
directions in the two legs of the at least one unipolar couple
element to establish a temperature differential across each of the
two legs of said unipolar couple element.
3. The device of claim 1, wherein said at least one unipolar couple
element is configured to generate at least one of an electrical
potential and an electrical current from a temperature differential
established across the two legs of said unipolar couple
element.
4. The device of claim 1, wherein the at least one unipolar couple
element comprises: a pair of p-type
Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice thermoelements.
5. The device of claim 4, wherein the p-type
Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice thermoelements have
a ZT of >1 at 300K.
6. The device of claim 1, wherein the at least one unipolar couple
element comprises: a pair of n-type
Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.3-xSe.sub.x superlattice
thermoelements.
7. The device of claim 8, wherein the n-type
Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.3-xSe.sub.x superlattice
thermoelements have a ZT >1 at 300K.
8. The device of claim 1, wherein the at least one unipolar couple
element comprises: a pair of n-type PbTeSe/PbTe superlattice
thermoelements.
9. The device of claim 8, wherein the n-type PbTeSe/PbTe elements
comprise: a pair of n-type PbTeSe/PbTe quantum-dot superlattice
thermoelements having a ZT of 1.6 at 300K.
10. The device of claim 1, wherein the at least one unipolar couple
element comprises: a pair of p-type PbTeSe/PbTe superlattice
thermoelements.
11. The device of claim 1, wherein the at least one unipolar couple
element comprises: at least one set of p-p and one set of n-n
unipolar couple elements.
12. The device of claim 1, wherein the at least one unipolar couple
element comprises: one set of p-p couples and two independent legs
of n.
13. The device of claim 1, wherein the at least one unipolar couple
element comprises: one set of n-n couples and two independent legs
of p.
14. The device of claim 1, wherein the unipolar couple elements
comprise a p-p bulk couple.
15. The device of claim 1, wherein the unipolar couple elements
comprise a n-n bulk couple.
16. The device of claim 1, wherein the unipolar couple elements are
configured to produce temperature differentials in a range from 1K
to 200K.
17. The device of claim 1, further comprising: a thermal insulation
between said first-temperature stage and said third-temperature
stage.
18. The device of claim 17, wherein the thermal insulation
comprises at least one of aerogels and polymer sheets.
19. The device of claim 1, further comprising: a controller
configured to control a temperature of the second-temperature stage
to produce desired source and drain temperatures on the
first-temperature stage and the third-temperature stage,
respectively.
20. The device of claim 19, wherein said controller is configured
to control said current flow to produce said desired source and
drain temperatures.
21. The device of claim 1, wherein said temperature differential
across each leg of said two legs is about half a temperature
differential between the first-temperature stage and the
second-temperature stage.
22. The device of claim 1, wherein at least one of the
first-temperature stage and the second-temperature stage comprises
a split header.
23. The device of claim 1, wherein said third-temperature stage is
configured to operate at a temperature about 100.degree. C. so that
a phase change of water to steam provides heat removal and said
first-temperature stage is configured to operate at a temperature
below 40.degree. C.
24. The device of claim 1, wherein said third-temperature stage is
configured to operate at a temperature about 100.degree. C. so that
a phase change of water to steam provides heat removal and said
first-temperature stage is configured to operate at a temperature
below 10.degree. C. or below.
25. The device of claim 1, further comprising: a water-based closed
cycle heat removal system connected to the third-temperature
stage.
26. The device of claim 1, wherein the at least one unipolar couple
element comprises: a p-p couple with each leg of said two legs
having at least one of a different material composition and a
different structure from the other leg.
27. The device of claim 26, wherein the p-p couple comprises: a
p-type Bi.sub.1.0Sb.sub.1.0Te.sub.3 thermoelement; and a p-type
Bi.sub.0.5Sb.sub.1.5Te.sub.3 thermoelement.
28. The device of claim 26, wherein the p-p couple comprises: a
p-type 10 Angstrom/30 Angstrom Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3
superlattice thermoelement; and a p-type 10 Angstrom/50 Angstrom
Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice thermoelement.
29. The device of claim 1, wherein the at least one unipolar couple
element comprises: a n-n couple with each leg of said two legs
having at least one of a different material composition and a
different structure from the other leg.
30. The device of claim 29, wherein the n-n couple comprises: an
n-type Bi.sub.2Te.sub.2.5Se.sub.0.5 thermoelement; and an n-type
Bi.sub.2Te.sub.2.85Se.sub.0.15 thermoelement.
31. The device of claim 29, wherein the n-n couple comprises: an
n-type 10 Angstrom/30 Angstrom
Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.2.85Se.sub.0.15 superlattice
thermoelement; and an n-type 10 Angstrom/50 Angstrom
Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.2.85Se.sub.0.15 superlattice
thermoelement.
32. A thermoelectric device comprising: at least one unipolar
couple element having two legs of a same conductivity type; an
intermediate-temperature stage connected between said legs of the
at least one unipolar couple element; and electrical contacts to
each leg of the unipolar couple element.
33. The device of claim 32, wherein said at least one unipolar
couple element is configured such that current flows in opposite
directions in the legs of the at least one unipolar couple element
to establish a temperature differential across the two legs of said
unipolar couple element.
34. The device of claim 32, wherein said at least one unipolar
couple element is configured to generate at least one of an
electrical potential and an electrical current from a temperature
differential established across the two legs of said unipolar
couple element.
35. The device of claim 32, wherein the at least one unipolar
couple element comprises: a p-p couple with each leg of said two
legs having at least one of a different material composition and a
different structure from the other leg.
36. The device of claim 32, wherein the at least one unipolar
couple element comprises: a n-n couple with each leg of said two
legs having at least one of a different material composition and a
different structure from the other leg.
37. A thermoelectric device comprising: at least a
four-temperature-terminal device including, a p-p unipolar couple
element having legs of a p-type electrical conductivity, a first
intermediate temperature stage connected across said legs of the
p-p unipolar couple element, a n-n unipolar couple element having
legs of an n-type electrical conductivity, and a second
intermediate temperature stage connected across said legs of the
n-n unipolar couple element and operated at a temperature different
than first intermediate temperature stage.
38. The device of claim 37, further comprising: electrical contacts
connecting to each of said legs of the p-p and said legs of the n-n
unipolar couple elements, said electrical contacts are connected
such that currents flow in opposite directions in each of the legs
of the p-p unipolar couple element and in each of the legs of the
n-n unipolar couple element to establish a temperature differential
across each of the p-p unipolar couple element and the n-n unipolar
couple element.
39. The device of claim 37, wherein said p-p unipolar couple
element and said n-n unipolar couple element are configured to
generate at least one of an electrical potential and an electrical
current from a temperature differential established across said p-p
unipolar couple element and said n-n unipolar couple element.
40. A thermoelectric device comprising: a heat source; means for
generating currents flowing in opposite directions in two legs of a
thermoelectric material of a same conductivity type, said means
coupled to said heat source; and a heat sink coupled to said two
legs and configured to dispose heat from said thermoelectric
device.
41. The device of claim 40, further comprising: an
intermediate-temperature stage connected across said two legs; and
a temperature controller configured to control a temperature of the
intermediate-temperature stage.
42. The device of claim 40, wherein said means for generating
currents comprise: a metal contact interposed between and
connecting to said two legs; two electrical contacts connected to
respective ends of said two legs opposite said metal contact; and a
voltage applicator configured to apply an opposite voltage
potential to respective of said electrical contacts.
43. The device of claim 40, wherein said means for generating
currents are configured to provide said currents to establish a
temperature differential across the two legs.
44. The device of claim 40, wherein said means for generating
currents are configured to generate, from a temperature
differential across said two legs, at least one of an electrical
potential and an electrical current.
45. The device of claim 40, wherein said means for generating
currents comprise: a p-p couple with each leg of said two legs
having at least one of a different material composition and a
different structure from the other leg.
46. The device of claim 40, wherein said means for generating
currents comprise: a n-n couple with each leg of said two legs
having at least one of a different material composition and a
different structure from the other leg.
47. A method for cooling an object, comprising: conducting heat
from the object to a thermoelectric device including a unipolar
couple element having two legs of a thermoelectric material of a
same conductivity type; and flowing currents in opposite directions
in said two legs to transport said heat across each of said legs in
a direction away from said object; and disposing of said heat from
the thermoelectric device through a heat sink into an ambient
environment.
48. The method of claim 47, further comprising: controlling a
temperature of an intermediate-temperature stage connected between
said legs.
49. The method of claim 47, wherein said flowing currents
comprises: applying opposite voltage potentials to respective of
two electrical contacts at ends of said two legs.
50. The method of claim 47, wherein said flowing currents
establishes a temperature differential across the two legs to cool
said object.
51. A method for thermoelectric power conversion, comprising:
extracting heat from a heat source coupled to a thermoelectric
device including a unipolar couple element having two legs of a
thermoelectric material of a same conductivity type; and
maintaining a temperature differential across the thermoelectric
device to a heat sink to produce electrical power from the
thermoelectric device; and dissipating heat from said heat sink
into an ambient environment.
52. The method of claim 51, further comprising: controlling a
temperature of an intermediate-temperature stage connected between
said legs to produce electrical power.
53. The method of claim 5 1, further comprising controlling a
temperature of an intermediate stage by introducing a fluid exiting
from a hot-stage coupled to the heat source onto the intermediate
stage.
54. The method of claim 53, wherein said controlling a temperature
mixes said fluid exiting from a hot-stage with a lower-temperature
fluid.
55. The method of claim 51, wherein said maintaining a temperature
differential generates at least one of an electrical potential and
an electrical current from the thermoelectric device.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the field of thermoelectric
devices and methods of manufacturing such devices.
BACKGROUND OF THE INVENTION
[0002] A thermoelectric device is capable of generating electricity
if two ends of the thermoelectric device are held at different
temperatures. When two dissimilar metals (conductors) or
semiconductors having different Seebeck potential or Fermi energy
levels are in contact at each end, a voltage is obtained if the
ends are at different temperatures (i.e., the Seebeck effect).
Conversely, an applied electrical current can induce a temperature
differential between the two ends due to the Peltier effect. The
Peltier effect causes absorption or liberation of heat when current
flows across the junction of two dissimilar materials. As electrons
flow from a p-type semiconductor to an n-type semiconductor an
energy gap or "hurdle" is traversed. Thermal energy is absorbed as
electrons overcome this energy hurdle, and this junction is cooled.
Conversely, as electrons flow from an n-type semiconductor to a
p-type semiconductor, electrons "fall" down the energy gap and thus
release heat. This release will locally heat the junction.
[0003] Thus, a thermoelectric device can be a cooler or a heat pump
which transfers heat by electric current. The principles of
thermoelectricity are utilized in power generation, thermocouples,
and refrigeration. The efficiency of a thermoelectric device can be
expressed in terms of a figure of merit (ZT). In order for a
material to be efficient for thermoelectric power conversion, it is
important to allow charge carriers to diffuse easily across
multiple Peltier couples while maintaining a temperature gradient.
That is, there must be a relatively high value for the Seebeck
coefficient (S), a high electrical conductivity (a), and a low
thermal conductivity (K). Current designs of commercially available
thermoelectric devices have efficiencies too low to warrant
widespread cooling application. However, improvements in the
thermoelectric material properties and thermoelectric device design
are expected to provide thermoelectric devices with enhanced
thermal performance. These devices will be better suited for power
generation, cooling, and temperature control applications.
[0004] Typically, a thermoelectric device contains p-type and
n-type semiconducting materials sandwiched between two ceramic
plates, for example an upper and lower faceplate or carrier plate.
The faceplates typically have high electrical resistivity and low
thermal conductivity. Situated between the faceplates are a number
of Peltier couples, formed by joining p-type and n-type
semiconductor elements. These couples can be arranged in a
two-dimensional array, thermally in parallel, and connected by
conductors (braze, solder, and the like) so as to be electrically
in series. Typically, a device being cooled is placed in thermal
contact with the cold faceplate, and a heat sink is placed in
contact with the hot faceplate.
[0005] Accordingly, a thermoelectric device technology typically
uses a bipolar, p-n couple with two temperature zones as shown in
FIG. 1. FIG. 1 depicts a conventional bipolar p-n couple 10 having
two legs 10a and 10b of opposite conductivity type. As shown, the
bipolar p-n couple 10 is configured with a polarity for cooling at
heat source 12. The legs 10 and 10b are connected electrically in
series and thermally in parallel such that current flow serially
through the legs 10a and 10b carries heat to heat sink 14 where the
heat is dissipated from the thermoelectric device. Consequently,
the bipolar p-n couple 10 utilizes two temperature zones connected
respectively to the heat source 12 and the heat sink 14. Fins 16,
as shown, are frequently utilized on either the heat source 12 or
the heat sink 16, if needed.
[0006] However, the utilization of different n and p-type materials
adds complications to the manufacturing process and frequently
costs efficiency of the fabricated thermoelectric device, as the
thermoelectric performance of one of the n and p-type materials is
typically lower the thermoelectric performance of the other of the
opposite type.
SUMMARY OF THE INVENTION
[0007] One object of the present invention is to provide unipolar
p-p or n-n couple avoiding the use of a complementary n-type and
p-type thermoelectric pair.
[0008] Another object of the present invention is to provide a
unipolar p-p or n-n couple with two electrical terminals and three
temperature terminals. As such, the present invention is a
departure from conventional thermoelectric device fabrication
utilizing a bipolar p-n couple with two electrical terminals and
two temperature zones.
[0009] A further object of the present invention is to provide a
device fabrication process which reduced the complexity of assembly
of modules.
[0010] Still, a further object of the present invention is to
provide higher efficiency thermoelectric devices by utilizing in
the thermoelectric devices the specific n- or p-type thermoelectric
material that has the better thermoelectric material
properties.
[0011] Thus, according to one aspect of the present invention,
there is provided a novel a thermoelectric device including at
least one unipolar couple element having two legs of a same
electrical conductivity type, a first-temperature stage connected
to one of the two legs, a second-temperature stage connected across
the legs of the at least one unipolar couple element, and a
third-temperature stage connected to the other of the two legs.
[0012] According to another aspect of the present invention, there
is provided a method for cooling an object. The method conducts
heat from an object coupled to the above-noted thermoelectric
device, flows currents in opposite directions in the two legs of
the thermoelectric device to transport the heat across each of the
legs in a direction away from the object, and disposes of the heat
into an ambient environment.
[0013] In still another aspect of the present invention, there is
provided a method for thermoelectric power conversion that extracts
heat from a heat source coupled to the above-noted thermoelectric
device, maintains a temperature differential across the
thermoelectric device to a heat sink, and dissipates heat from the
heat sink into an ambient environment. Maintaining the temperature
differential across the two legs generates electrical power from
thermoelectric device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] A more complete appreciation of the present invention and
many attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0015] FIG. 1 is a schematic illustration of a conventional p-n
couple having a configuration with a polarity for cooling a heat
source;
[0016] FIG. 2 is a schematic illustration according to one
embodiment the present invention of a three-thermal-terminal
(T.sup.3) p-p couple having a configuration with a polarity for
cooling a heat source;
[0017] FIG. 3A is a graph showing a .DELTA.T, temperature
difference, between a heat-sink and a heat-source versus current
flow in conventional bipolar couple;
[0018] FIG. 3B is a table showing a .DELTA.T, temperature
difference, between a heat-sink and a heat-source versus current
flow in conventional bipolar couple;
[0019] FIG. 4A is a graph showing a .DELTA.T, temperature
difference, between a heat-sink and a heat-source versus current
flow in a three-thermal-terminal p-p couple of the present
invention;
[0020] FIG. 4B is a table showing a .DELTA.T, temperature
difference, between a heat-sink and a heat-source versus current
flow in a three-thermal-terminal p-p couple of the present
invention; and
[0021] FIG. 5 is a schematic illustration according to another
embodiment of the present invention of an integrated p-p couple and
n-n couple thermoelectric module.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Referring now to the drawings, wherein like reference
numerals designate identical, or corresponding parts throughout the
several views, and more particularly to FIG. 2, FIG. 2 depicts a
trans-thermoelectric device 20 of the present invention. The
trans-thermoelectric device 20 includes a three-thermal-terminal
(T.sup.3) p-p couple element 22 shown in FIG. 2 as having a
configuration for cooling a heat source 24. The
trans-thermoelectric device 20, while shown having a p-p couple,
could instead be an n-n couple element. In either case, the
unipolar couple element 22 has two legs 22a of a same electrical
conductivity type. As shown in FIG. 2, electrical terminals 26
connected to respective ends of the two legs 22a on one side of the
unipolar couple element 22. The heat source 24 constitutes a
first-temperature stage connected to one of the legs 22a. A heat
sink/gate 28 constitutes a second-temperature stage and is
connected to a side of the unipolar couple element 22 opposite the
electrical terminals 26. A heat drain 30 constitutes a
third-temperature stage and is connected to the other leg of the
unipolar couple opposite the heat source 24, as shown
illustratively in FIG. 2. A configuration for power conversion
would be similar to that shown in FIG. 2, except that there would
be maintained a temperature differential between the heat source 24
and the heat drain 30, thereby inducing an electropotential on the
electrical terminals 26 and current flow through the unipolar
couple element 22.
[0023] The trans-thermoelectric device 20 in this embodiment
employs a unipolar p-p or n-n couple having two electrical
terminals and three temperature terminals, thereby achieving a
large temperature differential across each end of the unipolar
couple element 22. The trans-thermoelectric device 20 can be
considered as a three temperature zone device, and represents a
significant departure from a conventional bipolar p-n couple having
two electrical terminals and two temperature zones. The term
"Trans" is used herein to denote the effect of a "transfer thermal
effect" similar to the "transconductance" in a three-terminal
electrical transistor device. In this analogy, the present
invention represents a transition in thermoelectric device
technology much alike the transition in electronic device
technology from a two-terminal diode to a three-terminal
transistor. By the analogy, the present invention can be considered
a transition from a conventional p-n thermocouple (i.e. a thermal
diode) having two end temperatures, the source temperature and the
sink temperature, to a thermal triode having three end temperatures
(i.e., a source temperature, an intermediate-sink temperature, and
a drain temperature).
[0024] The above three-thermal-terminal p-p couple of the present
invention, as compared to a conventional two-terminal p-n couple,
utilizes two-stage pumping first from the heat source 24 to the
heat sink/gate 28, and then to the heat drain 30. By using this
approach, the present invention takes advantage of the higher
coefficient of performance (COP) of a p-type leg as compared to a
n-type leg, when operating as a heat pump, pumping heat from the
heat source 24 to the heat sink/gate 28, and then to the heat drain
30. The heat sink/gate 28 is maintained at a desired temperature,
somewhere between that of the heat source 24 and the heat drain 30.
Thus, the heat sink/gate 28 can be considered a gate whose
temperature, by adjustment (similar to the base of a bipolar
transistor or a gate of field-effect transistor), varies the
performance of the trans-thermoelectric device 20. So the present
invention can also be used in "an all thermal-logic" devices or
their applications. The fact that there is a trans-thermal effect
or a gate-control-like effect means that the temperature of the
gate 28 can be an equivalent thermal input for a thermal-logic
function and the temperatures at the source 24 and drain 30 can be
the output of the thermal-logic function.
[0025] Part of the role of the heat sink/gate 28 is to dissipate
from the trans-thermoelectric device 20 a fraction of the
waste-heat from heat source side. Thereby, one leg of the
trans-thermoelectric device 20 on the heat drain side does not have
to pump this fraction of waste-heat to the heat drain 30. The heat
sink/gate 28 provides a thermal path, but does not provide an
electrical path for current flow. Rather, current flows from the
heat source side p-leg to the heat drain side p-leg. As such, the
trans-thermoelectric device 20 uses both active cooling and heating
within the two legs 22a of the unipolar couple element 22,
simultaneously, to achieve a large .DELTA.Tmax in a single-stage
couple, thus expanding the use of thermoelectric device technology
and improving performance.
[0026] Fins 32, while shown in FIG. 2 at each of these temperature
zones, are optional. Thermal insulation 34, while shown in FIG. 2
between the heat source 24 element and the heat drain 30, is also
optional. The thermal insulation 34 could be formed by a vacuum
between the heat source/cold-side element and the heat
drain/hot-side element if feasible, or could be formed with a
low-thermal-conductivity medium (e.g., an aerogel having a thermal
conductivity of .about.0.02 to 0.05 W/m-K). Regardless, the thermal
insulation 34 serves to reduce the thermal transfer between the
heat drain and the heat source.
[0027] The trans-thermoelectric devices of the present invention
preferably utilize whichever one of p-type or n-type thermoelements
that has a higher figure-of-merit (ZT). For example, thermoelectric
devices and modules can be constructed using only p-type
Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice thermoelements with
a ZT of .about.2.5 at 300K, rather than combining with the p-type
thermoelements n-type Bi.sub.2Te.sub.3-based superlattice
thermoelements with a ZT of .about.1.2 to 1.9 at 300K to form a
conventional p-n couple. Similarly, the present invention can use
only n-type PbTeSe/PbTe quantum-dot superlattice thermoelements
with a ZT of .about.1.6 at 300K, rather than combining with n-type
thermoelements p-type PbTe-based superlattice thermoelements with a
much lower ZT at 300K. Similarly, unipolar couple elements can be
made of only bulk p-type Bi.sub.xSb.sub.2-xTe.sub.3 or n-type
Bi.sub.2Te.sub.3-xSe.sub.x. Indeed, the present invention opens up
thermoelectric device technology to thermoelectric material systems
where only one polarity (p-type or n-type) of material is good for
obtaining higher ZT in the temperature range of interest.
[0028] The two adjacent legs of the unipolar couple element 22, of
same polarity or conductivity type, need not be the same material.
For example, one p-type leg can be Bi.sub.1.0Sb.sub.1.0Te.sub.3 and
an adjacent p-leg can be Bi.sub.0.5Sb.sub.1.5Te.sub.3. Each of
these materials can be chosen based on the optimum property for
that temperature stage. Similarly, one p-type leg can be a 10
Angstrom/30 Angstrom Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice
and the adjacent p-leg can be 10 Angstrom/50 Angstrom
Bi.sub.2Te.sub.3/Sb.sub.2Te.sub.3 superlattice. Likewise, one
n-type leg can be an n-type Bi.sub.2Te.sub.2.5Se.sub.0.5
thermoelement, and an adjacent leg can be an n-type
Bi.sub.2Te.sub.2.85Se.sub.0.15 thermoelement. Similarly, one n-type
leg can be an n-type 10 Angstrom/30 Angstrom
Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.2.85Se.sub.0.15 superlattice
thermoelement, and an adjacent leg can be an n-type 10 Angstrom/50
Angstrom Bi.sub.2Te.sub.3/Bi.sub.2Te.sub.2.85Se.sub.0.15
superlattice thermoelement.
[0029] The use of unipolar trans-thermoelectric devices reduces the
complexity of assembly of modules, and reduces the need for perfect
matching of the thermal performance of the p-type and n-type legs
in the conventional bipolar couple. The use of unipolar p-p or n-n
transthermistor devices reduces the need for perfect matching of
the p and n legs. In a conventional p-n bipolar thermoelectric
device, the properties of the p- and n-legs have to be well known
to optimize the geometric properties or the aspect ratio of the two
legs. However, with the use of p-p or n-n unipolar couples in the
present invention, the matching is guaranteed by using the same
material for both the legs. The use of unipolar
trans-thermoelectric devices reduces the .DELTA.T per element (i.e.
across one p-element of a p-p couple) by about half, compared to
that which would exist in each element of a conventional p-n couple
for the same cold and hot-end temperatures. As such, thermal stress
is reduced in the trans-thermoelectric devices as compared to the
conventional two-terminal device for a fixed .DELTA.T between the
hot and cold-side temperatures. Alternatively, the use of unipolar
trans-thermoelectric device can increase the .DELTA.Tmax achievable
per couple significantly, over and above the conventional p-n
couple, thereby providing a higher coefficient of performance (COP)
for a fixed .DELTA.T between the hot and cold-side
temperatures.
[0030] For example, a conventional bipolar bulk p-n couple shows
.DELTA.Tmax of 58.8K, typical of most standard bulk
Bi.sub.2Te.sub.3-based TE technology. This data is shown in FIGS.
3A and 3B. FIGS. 3A and 3B are a graph and table showing a
.DELTA.T, temperature difference, between a heat-sink and a
heat-source versus current flow in a conventional bipolar couple.
The data shown in FIG. 3A was taken from p-n couples with aspect
ratios (ratio of height of element to area of element, in units of
cm.sup.-) of approximately 3 cm.sup.-1. Thus, the peak
.DELTA.T.sub.max shown in FIG. 3 occurs around 15 Amps, as
expected.
[0031] By contrast, FIG. 4A and 4B are a graph and table showing a
.DELTA.T, temperature difference, between a heat-sink and a
heat-source versus current flow in a three-thermal-terminal p-p
couple having similar aspect ratio elements to the conventional
bipolar couple measured in FIGS. 3A and 3B. FIG. 4A illustrates
that the trans-thermoelectric devices of the present invention can
achieve a .DELTA.T.sub.max of .about.155.7K across a three-terminal
unipolar, p-p, bulk couple. In the present invention, a ratio of
.DELTA.Tmax/cycle of current flow between heat-source and drain is
a figure of merit. The cold side (source) was at minus 6.2.degree.
C., and the hot-side (drain) was at plus 149.5.degree. C. in this
demonstration. The heat sink or gate was kept at .about.23.degree.
C. The data in FIGS. 4A and 4B also shows a more linear response,
due to the maintenance of the heat sink or gate at -23.degree. C.,
even with no forced heat-removal at the drain. If the drain had
been kept thermally managed to .about.100.degree. C., using for
example an air-fin arrangement, the cold-side (source) would be
even cooler than that shown in FIG. 4A. The table in FIG. 4B
depicts the highest .DELTA.T.sub.max observed for bulk p-type
Bi.sub.2-xSb.sub.xTe.sub.3 alloy thermoelements, with the I vs.
.DELTA.T being shown in bold for comparison for a given value of
current flow between the source and drain. The results in FIGS. 4A
and 4B employ p-type unipolar couples of
Bi.sub.0.4Sb.sub.1.6Te.sub.3, approximately 1 mm thickness, and
having a doping level about 3.times.19 cm.sup.-3. In the present
invention, a ratio of .DELTA.T.sub.max/cycle of current flow
between heat-source and drain is a figure of merit.
[0032] FIGS. 3A and 4A show that the present invention has been
able to achieve a .DELTA.T.sub.max of .about.155.7K across a
three-terminal unipolar, p-p, bulk couple. The cold side was at
minus 6.2.degree. C. and hot-side was at plus 149.5.degree. C. This
result was achieved with no forced heat removal from the hot-end of
the p-p, unipolar, transthermistor device. In contrast, the
conventional bipolar bulk p-n couple in FIG. 3A shows
.DELTA.T.sub.max of 58.8K, typical of most standard bulk
Bi.sub.2Te.sub.3-based TE technology.
[0033] The unipolar devices of the present invention have other
advantages besides coefficient of performance (COP). The hot-side
of the p-p or n-n unipolar couple can now be operated at a much
higher temperature, thereby making heat-removal for a given ambient
temperature easier. For example, in a conventional bipolar p-n
couple, a current of 2 Amps leads to a cold-side of 3.9.degree. C.
(from a no-current value of 22.1.degree. C.), with hot-side of
22.degree. C., and thus a .DELTA.T of 18.1.degree. C. In contrast,
in a unipolar p-p couple, a 2 Amp current leads to a cold-side of
2.5.degree. C. (from a no-current value of 22.4.degree. C.) and a
hot-side of 61.9.degree. C., and thus a .DELTA.T of 59.4.degree.
C., providing more than a factor of three increase in the
temperature differential of the unipolar p-p couple as compared to
the conventional bipolar p-n couple for the same drive current.
Accordingly, in the present invention, the unipolar couple elements
can produce temperature differentials (depending on the magnitude
of current flow) in a range from 1K to 200K.
[0034] Furthermore, consider for example an ambient temperature of
18.degree. C. For an ambient of 18.degree. C., it is easier to
dissipate heat from a hot-side of 59.4.degree. C. of the unipolar
p-p couple than from a hot-side of 22.degree. C. in a conventional
bipolar -n couple. The larger temperature difference between the
heat-drain and the ambient will permit the use of for example
smaller and/or quieter cooling fans. In addition, the ability to
raise the drain temperatures such as 149.5.degree. C. permits the
present invention to utilize phase-change heat-transfer solutions,
using a high-heat-transfer coefficient liquid like water, while
still being able to achieve -6.degree. C., sufficient for cooling a
cold-finger for refrigeration or air-conditioning purposes.
[0035] The trans-thermoelectric devices of the present invention
are expected to be useful in monolithic electronic/optoelectronic
chip technology cooling where heat is taken from certain
heat-sensitive spots and deposited at different, non-heat-sensitive
spots on the chip, and is expected to be useful in cooling infrared
devices including infrared countermeasure devices and infrared
simulation devices.
[0036] According to the present invention, the use of only p-p or
n-n unipolar couples in a module format (e.g., the use of multiple
sets of p-p or n-n couples) can be implemented with reduced thermal
transfer losses, through any electrical interconnection between the
drain and source by metallic wires, by making sure that the
electrical connections are made suitably after a thermal
equilibration to ambient temperatures. For example, the electrical
lead from the drain can be taken through a point of thermal
equilibrium temperature, corresponding to the equilibration between
the heat sink (where heat is to released) and the thermoelectric
device point labeled as drain, and then sent through a point of
thermal equilibrium temperature, corresponding to the equilibration
between the heat source (where heat is to be absorbed) and the
thermoelectric device point labeled as source. Such issues are not
present if two or more p-p couples are operated electrically in
parallel (and thermally parallel as well) or similarly if two or
more n-n couples are operated electrically in parallel (and
thermally in parallel as well).
[0037] The p-p unipolar couple of the present invention can be used
in conjunction with an n-n unipolar couple for ease of integration
into a modular device. As such, it is possible that the heat-sink
temperatures for the respective unipolar couple elements can be
different. Under this situation, the present invention would have
four temperature terminals (a heat source, a heat drain, a
heat-sink/gate of n-type, and a heat-sink/gate of p-type) and two
electrical terminals.
[0038] FIG. 5 is a schematic illustration of an integrated p-p
couple and n-n couple thermoelectric module 50. A module
constructed with a set of p-p couples 52 or n-n unipolar couples 54
and 64 is shown in FIG. 5. The first unipolar, n-n couple 54 shown
on the left has three temperature zones--heat source 56, heat
member 58, and heat sink/gate 60. The first unipolar, p-p couple 52
shown to the right of the first unipolar, n-n couple 54 has three
temperature zones--heat member 58a, heat member 58b, and heat
sink/gate 62. The second unipolar, n-n couple 64 shown to the right
of the first unipolar, p-p couple 52 has three temperature
zones--heat member 58b, heat drain 66, and heat sink/gate 68. Fins
70, although optional, are shown at each of these temperature
zones. The fins 70 can be replaced with high thermal conductivity
heat spreaders. Thermal insulation 72, as noted above, can be used
depending on the dissimilarity of performance between the n- and
p-materials. Thus, the heat-sink temperature joining two adjacent
n-legs can be different from the heat-sink temperature joining two
adjacent p-legs.
[0039] As such, the present invention can utilize multiple
temperature stages. For example, a temperature zone corresponding
to for example heat sink/gates 60, 62, and 68 in FIG. 5 need not be
physically continuous. Rather, in one embodiment of the present
invention, each block of a particular temperature zone, is attached
to a respective common block, which essentially will represent a
tiled or split stage. This is advantageous for reducing thermal
stress issues as the various temperature zones can be managed with
better accommodation for thermal expansion relief.
[0040] The present invention can utilize a counterflow of
heat-transfer fluids at the source and drain sides to facilitate
optimal heat-transfer processes. That is the flow of heat-transfer
fluids through the various drain contacts is in a direction
opposite to that through the respective source contacts, minimizing
the .DELTA.T across each of the device couple. As seen from the
data in FIG. 4, a reduced .DELTA.T implies less current and hence
less power. Thus, for the same external .DELTA.T needed at a system
level which implies certain temperatures of inlet and outlet
heat-transfer fluids, the present invention can operate the
individual thermoelectric p-p couple or n-n couple at lower
temperatures. Hence, in the present invention, a temperature of an
intermediate stage can be controlled by fluids that exit from a
hot-stage. Consequently, these fluids would have dropped in
temperature, and perhaps can be mixed with a lower-temperature
fluid.
[0041] The concepts illustrated by the present invention can be
used with bulk thermoelectric (ZT.about.1 at 300K) technology to
potentially achieve a coefficient of performance (COP), for a given
.DELTA.T, of a factor of two or better than the conventional p-n
couple-based modules. Similarly, utilizing superlattice
thermoelectric (ZT.about.2.4 at 300K) technology in conjunction
with the present invention is expected to achieve COP approaching
that of freon-based mechanical systems. The approach of the present
invention permits a factor of two better material utilization in
the fabrication of thin-film thermoelectric modules. The present
invention can be enhanced further with superlattice p-type
thermolements and/or n-type superlattice thermoelements. The
present invention is not limited to any particular type of
material. Rather, the present invention is applicable to any bulk
or thin-film thermoelectric material regardless of operating
temperatures.
[0042] The present invention has applicability to numerous
thermoelectric device applications, including cooling/heating, and
those applications discussed in U.S. application Ser. No.
10/118,236, entitled "THIN FILM THERMOELECTRIC COOLING AND HEATING
DEVICES FOR DNA GENOMIC AND PROTENIC CHIPS, THERMO-OPTICAL
SWITCHING CIRCUITS, AND IR TAGS", the entire contents of which are
incorporated herein by reference and power conversion, where local
selective heating and cooling on surfaces is utilized to engineer
DNA genomic and protein chips, to produce thermooptical switching
circuits, and to produce infrared tags. In such applications,
thermoelectric cooling and heating devices are provided with a
substrate and a plurality of thermoelectric elements arranged on
one side of the substrate to perform at least one of selective
heating and cooling. Each thermoelectric element includes a
thermoelectric material, a Peltier contact contacting the
thermoelectric material and forming under electrical current flow
at least one of a heated junction and a cooled junction, and
electrodes configured to provide current through the thermoelectric
material and the Peltier contact. As such, the thermoelectric
cooling and heating devices selectively bias each individual
thermoelectric element on the device to provide on one side of the
thermoelectric device a grid of localized heated or cooled
junctions. In such application, the unipolar couple elements of the
present invention can be used as the above-noted thermoelectric
element.
[0043] The present invention can utilize the phonon-blocking
electron structures described in U.S. Ser. No. 10/265,409 entitled
"PHONON-BLOCKING, ELECTRON-TRANSMITTING LOW-DIMENSIONAL
STRUCTURES", the entire contents of which are incorporated by
reference, to enhance the materials performance of the
thermoelectric materials in the legs of the unipolar couple element
of the present invention. In phonon-blocking structures,
thermoelectric structures include at least first and second
material systems having different lattice constants and interposed
in contact with each other, and a physical interface at which the
at least first and second material systems are joined with a
lattice mismatch and at which structural integrity of the first and
second material systems is substantially maintained. The first and
second material systems have a charge carrier transport direction
normal to the physical interface and preferably periodically
arranged in a superlattice structure. The first and second material
systems in contact with each other have a lattice mismatch in a
plane perpendicular and/or in a plane parallel to a central axis
common to both materials systems. A periodicity of the at least
first and second material systems is configured to reduce thermal
conduction in a direction along the periodicity. The perpendicular
plane is substantially normal to an electrical carrier transport
direction in the device, and the lattice mismatch provides an
acoustic mismatch to reduce the thermal conduction along the
electrical carrier transport direction.
[0044] The present invention has applicability to the cascade
thermoelectric device applications described in U.S. Ser. No.
09/812,811 entitled "CASCADE CRYOGENIC THERMOELECTRIC COOLER FOR
CRYOGENIC AND ROOM TEMPERATURE APPLICATIONS", the entire contents
of which are incorporated by reference, where cascades of
thermoelectric devices are utilized to produce cascade coolers with
a range of operational temperatures from cryogenic to room
temperature applications. In such application, a cascade
thermoelectric cooler integrates high performance\high-ZT
Bi.sub.xSb.sub.2-xTe.sub.3 and Bi.sub.2Te.sub.3-xSe.sub.x-based
super-lattice-structure thin-film thermoelectric devices with a
bulk-material based thermoelectric cooler including plural cascaded
cold stages with each successive cascaded cold stage able to cool
to a progressively lower temperature. Each cold stage in the
bulk-material thermoelectric cooler includes a heat source plate, a
heat sink plate, p-type thermoelectric elements, and n-type
thermoelectric elements. Moreover, the thin film thermoelectric
cooler can have multiple stages which each stage contains a heat
source plate, a heat sink plate, p-type super-latticed
thermoelectric elements, and n type super-latticed thermoelectric
elements. By attaching an output heat source plate on the thin-film
thermoelectric cooler to an input heat sink plate on the
bulk-material thermoelectric cooler, the integration of the thin
film thermoelectric with the bulk-material-based thermoelectric
yields a cascade thermoelectric cooler wherein the
bulk-material-based thermoelectric cooler cools to 170-200 K and
the thin-film thermoelectric device cools to cryogenic temperatures
between 70 and 120 K. Another level of thin-film super-lattice
integration can achieve temperatures near 50 K. The cascaded
devices as such can employ the unipolar couple elements of the
present invention rather than the conventional p-n thermoelectric
pair.
[0045] Accordingly, in one embodiment of the present invention,
there is provided a method for cooling an object. The method
conducts heat from an object coupled to the trans-thermoelectric
device of the present invention, flows currents in opposite
directions (i.e. opposite current flow) in the two legs of the
thermoelectric device to transport the heat across each of the legs
in a direction away from the object, and disposes of the heat from
the thermoelectric device into an ambient environment. Further, as
noted above, a temperature of an intermediate-temperature stage
connected between the two legs can be controlled to accordingly
control the performance of the thermoelectric device. The opposite
current flow can be established by applying opposite voltage
potentials (i.e. by a voltage applicator) to respective of two
electrical contacts at ends of the two legs. The opposite current
flow establishes a temperature differential across the two legs to
thereby cool the object.
[0046] Complementarily, there is provided by the present invention
a method for thermoelectric power conversion. The method extracts
heat from a heat source coupled to the above-noted
trans-thermoelectric device, maintains a temperature differential
across the thermoelectric device to a heat sink, and dissipates
heat from the heat sink into an ambient environment. Maintaining
the temperature differential across the two legs produces
electrical power (i.e. at least one of an electrical potential and
an electrical current) from thermoelectric device. Further, the
method can control a temperature of an intermediate-temperature
stage connected between the legs to produce electrical power for
example by controlling a temperature of an intermediate stage by
introducing a fluid exiting from a hot-stage coupled to the heat
source onto the intermediate stage. The fluid temperature can for
example be controlled by mixing the fluid exiting from the
hot-stage with a lower-temperature fluid.
[0047] Accordingly, in a further embodiment of the present
invention, there is provided a thermoelectric device having a heat
source, a mechanism coupled to the heat source to generate current
flows in opposite directions in the two legs of a thermoelectric
material of a same conductivity type, and a heat sink coupled to
the mechanism to dispose of heat from the thermoelectric device.
The thermoelectric device can include an intermediate-temperature
stage connected between the two legs, and a mechanism to control a
temperature of the intermediate-temperature stage. One example of a
mechanism coupled to the heat source to provide current flows in
opposite directions (i.e. opposite current flow) includes a metal
contact interposed between and connecting to the two legs, two
electrical contacts connected to respective ends of the two legs
opposite said metal contact upon which an opposite voltage
potential is applied to respective of the electrical contacts. In
this example, the opposite current flow through the two legs
establishes a temperature differential across the two legs. In
another example, a temperature differential across the two legs
generates the opposite current flow.
[0048] Numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *